27x^3+125=0.... so factor the left side
(3x+5)(9x^2-15x+25)=0
Now split each side
(3x+5)=0
(9x^2-15x+25)=0
And solve each one separably.
For the first one: (3x+5)=0 ... subtract 5 and then divide by 3
You get x=-5/3
Now solve the other part using the quadratic equation.